Cytokines regulate the expression of other cytokines in the centrally derived rat C6 glioma cell line. However, the modulation of tumor necrosis factor-α (TNF-α, a pivotal proinflammatory cytokine) in C6 cells is unknown. Here we investigated the expression of TNF-α mRNA in C6 glioma cells in response to TNF-α, interleukin-1β (IL-1β), IL-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), and interferon-α (IFN-α). The data show that (1) IL-1β induced a significant upregulation of TNF-α mRNA; (2) the effect of IL-1β on TNF-α mRNA expression was completely blocked by the concomitant application of IL-1Ra, which suggests specificity of IL-1β action through the IL-1 signaling receptor; (3) no detectable modulation of TNF-α mRNA expression was observed with the individual applications of TNF- α, IL-6, or IFN-α; (4) the concomitant treatments of TNF-α + IL-1β or TNF-α + IL-1β + IL-6 strongly upregulated TNF-α mRNA expression, whereas the concomitant application of TNF-α + IL-6 or IL-1β + IL-6 induced a moderate increase; and (5) IFN-α significantly attenuated induction of TNF- α mRNA by TNF-α + IL-1 β + IL-6. Thus, IL-1β, TNF-α and IL-6 interact to upregulate TNF-α mRNA expression synergistically, and IFN-α acts as an inhibitory cytokine in C6 glioma cells. These findings also suggest that the rat C6 glioma cell line may be used as an in vitro model to characterize cytokine-cytokine interactions.
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